This study proposes to examine the acceptance and function of the frozen bone allograft in both the dog and rat in orthotopic bone graft sites. The functional and histologic result will be examined in relationship to poorest and best histocompatibility matching in the dog using an ulnar segmental replacement model. In addition the effect of a clinically usuable immunosuppression program will be studied to determine if this will significantly improve the short or long term results as evaluated by both histologic and biomechanical strength of the grafted bone. In parallel the study will examine both the dog and rat after frozen bone allografting for the existence of both humoral and cellular cytotoxic immunity. Further the influence of the bone grafts on skin and ovarian allografts across both weak and strong histocompatibility barriers will be studied and an effort made to determine whether serum factors or some sub-population of lymphoid cells can be demonstrated to be responsible for the effects found.